A payload header suppression (PHS) method is defined in IEEE 802.16 standard. In the PHS method, a header is divided into a suppression part and a non-suppression part. First, a transmitter sends the non-suppression part by eliminating the suppression part of the header into a receiver. Then, the receiver restores the eliminated suppression part of the header and forms the entire header. Thus, a predetermined header suppression rule is exchanged between the transmitter and the receiver at call setup step.
FIG. 1 illustrates a protocol structure of wireless telecommunication network providing a packet service based on Internet Protocol (IP) in a general IEEE 802.16 system. Referring to FIG. 1, the protocol structure will be described from an upper layer to a lower layer.
A data flows from a multimedia applications layer 113 into lower layers. The data is transmitted into a real-time transport protocol (RTP) layer 110, a hypertext transport protocol (HTTP) layer 111, and a file transport protocol (FTP) layer 112 based on a kind of the multimedia applications layer. Herein, the multimedia applications layer is considered as a web browser in present invention. However, the present invention will be applied similarly to other multimedia applications layer.
The data from the web browser is transmitted into the HTTP layer 111 and transformed into a data having an HTTP format in the HTTP layer 111. Then, the data having the HTTP format is transmitted into a transmission control protocol (TCP) layer 109.
The TCP layer 109 adds a TCP header to the received data and transmits the TCP header added data into an Internet protocol (IP) layer 107. The IP layer 107 adds an IP header to the received data and transmits the IP header added data into a convergence sublayer—service access point (CS-SAP) 106.
The CS-SAP 106 transmits the received data into a convergence sublayer (CS) 105. In the CS 105, a packet classifier 104 classifies the received packet based on a predetermined classification condition. The predetermined classification condition includes an IP address of the transmitter, an IP address of the receiver and a TCP port. The above values are defined in the IP header and the TCP header. Therefore, the packet classifier 104 extracts the above values from the header of the received packet.
After the classification of the received packet is completed, the packet classifier 104 examines whether a header suppression rule of the received packet is set up or not, and transmits the received packet into a header compressor 103.
The header compressor 103 compresses the header of the received packet based on the predetermined header suppression rule. When the header suppression rule is not set up, the header compressor 103 does not compress the header of the received packet.
After the header compression of the received packet is completed, the CS 105 maps the compressed packet based on a predetermined flow determined at the call setup step, adds a connection identifier (CID) and transmits the CID added packet into a media access control (MAC) sublayer 101 through a media access control—service access point (MAC-SAP) 102.
In the protocol structure, data receiving and data processing are performed in the receiver to the contrary of data transmitting and data processing in the transmitter.
Referring to FIGS. 2 to 3, a packet transmitting and a packet receiving based on the PHS method in the IEEE 802.16 system will be described.
FIG. 2 is a flowchart illustrating a header suppression procedure of a transmitter in the general IEEE 802.16 system.
First, a packet is received from an upper layer at step S201. The transmitter classifies the packet at step S202. Then, five parameters for suppressing the header of the classified packet is extracted at step S203. Herein, the five parameters are designated as a packet header suppression rule.
1. PHS field (PHSF)
2. PHS index (PHSI)
3. PHS mask (PHSM)
4. PHS size (PHSS)
5. PHS verify (PHSV)
The packet header suppression rule is predetermined between a base station and a terminal at call setup step.
The transmitter determines whether a packet verification is performed or not by checking the PHSV at step S204. When a value of the PHSV is ‘1’, the transmitter determines that the packet verification should be performed.
In step S204, if the packet verification is determined, step S205 is performed. If the packet verification is not determined, step S207 is performed.
At step S205, the transmitter verifies the packet based on the PHSF and the PHSM.
When the packet verification is performed successfully, step S207 is performed. When the packet verification is failed, step S208 is performed.
Subsequently, at step S207, the transmitter compresses the verified packet by eliminating bytes based on the PHSM and sets the PHSI of the verified packet as ‘1’.
However, the transmitter does not compress the verification failed packet and sets the PHSI of the verification failed packet as ‘0’ at step S208.
A value of the PHSI determined at step S207 or S208 is added into the received packet at step S209 and the PHSI added packet is transmitted into the MAC layer 101 through the MAC-SAP 102 at step S210.
FIG. 3 is a flowchart illustrating a header restoration procedure of a receiver in the general IEEE 802.16 system.
The receiver receives a packet from a lower layer through the MAC-SAP 102, reconstructs the received packet based on the packet header suppression rule and transmits the reconstructed packet into the upper layer CS 105.
When the packet is received from the MAC layer 101 throughout the MAC-SAP 102 at step S301, the CS 105 extracts the PHSI added in received packet and acquires the CID of the received packet at step S302.
Subsequently, the receiver acquires the PHSF, PHSM, PHSS and PHSV of the received packet at step S303 and reconstructs eliminated header based on the five values of the packet header suppression rule at step S304.
The reconstructed packet is transmitted into the upper IP layer 107 through the CS-SAP 106 at step S305.
FIG. 4 is a diagram illustrating header elimination and restoration procedure based on a header suppression technique in the IEEE 802.16 system.
As shown in FIG. 4, the transmitter eliminates a header 411 of a transmission packet 401 based on values of the PHSM 402. For example, if a value of the PSHM is set up as ‘1’, corresponding bytes of the transmission packet 401 are eliminated. That is, the transmitter determines that which parts of the header are eliminated based on the value of the PHSM.
The remnant header i.e., actual transmitting header 408 includes bytes which is not set up as ‘1’ in the PHSM 402. Therefore, transmitting packet 404 is simplified in an actual wireless channel.
In the wireless channel, the receiver receives the transmitting packet 404 and restores the packet based on the PHSM used for compressing in the transmitter. The receiver decides that a part is set up as ‘1’ in the PHSM 405 as a restoration part. After determining the restoration part, the receiver restores the header 412 perfectly by combining a PHSF 406 and the received suppressed header, i.e., the actual transmitting header 408. The receiver transmits the resorted packet 407 into the upper layer.
Herein, a header may be partially eliminated or not. When the header is not eliminated, PHSI is set up as ‘0’ in CS 105 and added to the transmission header, and PHSI added packet is transmitted into the MAC layer 101. However, when the header is eliminated, PHSI is set up as not ‘0’ and added to the suppressed header, and PHSI added packet is transmitted into the MAC layer 101.
FIG. 5 is a diagram illustrating an overhead of header information in an IPv4 communication system.
A general method for generating the packet header suppression rule will be described referring to FIG. 5.
As shown in FIG. 5, header information includes IP header information for supporting the IPv4, UDP header information for supporting the UDP and RTP header information for supporting the RTP.
In FIG. 5, parameters of the header information are classified into fields varying in every packet 504 and 505, fields not varying in every packet 501 and fields occasionally varying after call setup 502 and 503. Here, since the fields of the header information have no connection with the present invention, detailed description of the parameters will be omitted.
The packet header suppression rule is set up based on the fields not varying in every packet 501. That is, it means that the header information for setting the packet header suppression rule is predetermined and programmed by a programmer.
For example, the fields not varying in every packet such as an address of transmitter, an address of target and a port number are predetermined programmed and constructed the packet header suppression rule statically by the programmer. Since, the packet header suppression rule is set up at call setup step, the header of packet transmitted after the call setup can be suppressed.
In IEEE 802.16 standard, the payload header suppression (PHS) method is defined and used for reducing size of the packet header in wireless channel.
In the PHS method, a header is divided into a suppression part and a non-suppression part. First, a transmitter sends the non-suppression part into a receiver by eliminating the suppression part of the header. Then, the receiver restores the eliminated suppression part of the header and forms the entire header.
However, the PHS method of the IEEE 802.16 standard has several problems as described below.
First, in fields of header, there are fields varying in every packet, fields not varying in every packet and fields occasionally varying after call setup. Therefore, the fields occasionally varying after call setup cannot be eliminated based on the PHS method of the IEEE 802.16 standard.
Second, applications such as a media player and a web browser can change an access server in working. Therefore, detecting method of new connection between new access server and the applications is needed.
Third, when the programmer predetermines a programming that the packet header suppression rule is set up by selecting fields of header information not varying in every packet statically, the fields not varying in every packet among the header information still can be exist and it cannot be eliminated perfectly. For example, if the programmer sets the packet header suppression rule based on the IP header information and the UDP header information, fields not varying in every packet of the RTP header information cannot be eliminated in a header, which includes the IP header information, the UDP header information and the RTP header information.